This invention relates in general to solar cells and in particular to a new and useful thin film solar cell having a n-i-p structure which comprises a substrate having a roughened substrate surface with an n-layer for light entering the cell and wherein the surface consists mostly of concave surface portions with no sharp points.
Solar cells are to convert the greatest possible part of the irradiated light energy into electrical energy. In solar cells such as thin film solar cells of a-Si the light of the long wave spectral range is not absorbed completely. A part of the light not absorbed is reflected by a metallic backside contact and can be utilized again in the solar cell. To obtain the longest possible optical path for this reflected light in the active solar cell layer it is known to reflect the light not perpendicularly, but at a flat angle; this is achievable by using a suitably structured backside electrode ("light trapping"). The short-circuit current of the solar cell is increased in this manner (Journal I. Vac. Sci.Technol., Al(2), 1983, pages 578, 582).
The charge carrier drift plays a big role in a-Si solar cells (n-i-p cells). Therefore, the electric field curve in the solar cell is important. The electric field should be as uniform as possible inside the solar cell and should nowhere assume the value zero, otherwise the recombination of the charge carriers would be increased or the capture length reduced, and the fill factor would drop (Appl. Phys. Lett. 44 (5), 1984, pages 437-539).